SGU SVM Anatomy 2: Equine Head

Changes in Equines during physical exertion

--Nostrils dilate maximally --Vascoconstriction of cavernous tissues in nasal submucosa --Dilation of nasal meatuses (especially middle and ventral) --Arytenoid cartilages are maximally abducted --Increase in size of area of rim glottidis --Vestibular and vocal folds are in full abduction during both inspiration and expiration

Incisive Duct

--Paired tube in the floor of the nasal cavity --Connects nasal cavity with the oral cavity Nasal Opening Ventral meatus at the level of the canine tooth Oral Opening In incisive papilla

Boarders of Viborg's triangle

--Angle of mandible --Tendon of sternocephalicus --Linguofacial vein

Caudal Portion of Vestibule

--Cilated pseudostratified --Contains ethmoidal conchae

UNIQUE: Horse Ventral Nasal Sinus

--Divided into rostral and caudal parts by septum --Caudal part forms ventral conchal sinus

UNIQUE: What makes the dorsal concha different in the horse?

--Entirely coiled --Divided into rostral and caudal parts by a septum --Caudal part is enclosed by the dorsal conchal sinus

What important structures have a relationship with the ventral part of the guttural pouch?

--External carotid artery --Lateral and medial retropharyngeal lymph nodes

What important structures have a relationship with the roof/dorsal part of the guttural pouch?

--Foramen lacerum (part of meninges of brain) --CN 9-12 --Chorda tympani --Sympathetic truck beyond the cranial cervical ganglion --Internal carotid artery

EQUINE DENTITION

--Ideally suited to diet of abrasive grass --40 teeth in total --Anisognathous jaw

CLINICAL: Paranasal sinuses

--Infection prone --Equine dentistry --Dehorning procedures in ruminants

Middle Portion of Vestibule

--Lined by ciliated pseudostratified epithelium --Contains the dorsal and ventral conchae

When does the Galvayne's groove appear?

--Longitudinal depression on the labial surface of the upper corner incisor --First appears at the gum line at 10 years

What is the guttural pouch?

--Membranous sac that is an extension of the auditory tube --Larger medial compartment which folds over stylohyoid bone to create two compartments

Frontal Sinus

--Present in all domestic animals, b/w cranial and nasal cavity and orbit --Extends rostrally into dorsal turbinate bone --Single cavity partly separated by bony lamellae

Why is the horses mouth narrow?

--Roots and crowns of cheek teeth (especially in young animals) --Nasal and ethmoid conchae --Pneumatized bones --Thick mucosa

First Portion of Vestibule

--Stratified squamous epithelium

CLINICAL: Criteria and features used for aging

1. Eruption information 2. Wearing features of incisor teeth --> Cup disappearance --> Dental star appearance --> 7-year hook --> Galvaynes groove

Maxillary Sinus

1. Rostral maxillary sinus 2. Caudal maxillary sinus --Separated by oblique septum, situated about 5cm, from rostral end of facial crest

Eruption of Permanent Canine

4-5 years

Eruption of Permanent 1st premolar

5-6 months

When does the cup disappear generally?

8 years old, and enamel spot forming the bottom of the cup remains

Paranasal Sinuses

Air filled diverticula from nasal cavity lined w/ mucosa --Invaginations of nasal epithelium into adjacent bones and some nasal conchae Conchofrontal Sinus Maxillary Sinus

NOSE

Apex Nasal Septum

Spatulate

Apex of the tongue

CLINICAL: Purpose of floating

As a result of anaisognathism --Vestibular side of lower teeth wear faster than lingual side BUT lingual side of upper teeth wear faster leading to sharp edges Require floating to eliminate them, or they will injure the tongue and cheek

Turbinate vs. Original Part of Sinuses

As the concha run within the sinuses, they create their own little sinuses, making each sinus have both a medial turbinate part, and lateral original part Rostral Maxillary Sinus Incorporates ventral conchal sinus/turbinate Frontal Sinus Incorporates dorsal conchal sinus/turbinate

Enamel spot vs. Dental Star

As the teeth wear away, they show... Enamel Spot Presence of infundibulum or cup, little dark spot Dental Star Secondary darker dentine that fills the pulp cavity, aging mechanism

UNIQUE: What makes the sublingual caruncle different?

At level of canine teeth, it only has one duct because there is no monostamatic duct of the sublingual salivary gland

Respiratory Rate of Equines

At rest 8-12 per minute Exercise 150 per minute

CLINICAL: Why is the horse an obligate nasal breather?

Because the relationship of the soft palate with the oropharynx makes it very difficult to breathe through its mouth

CLINICAL: Wolf teeth

Can be problematic, often removed even if they do erupt

Which teeth have no infundibula?

Canine and Cheek teeth

What teeth are not hyposodont in equines?

Canine and P1

Which teeth only sometimes develop?

Canines Stallion: All 4 canines are present Mares: May be absent or poorly developed First Premolars Usually do not develop in either gender but when they do present in upper arcade called Wolf teeth.

Dorsal lingual cartilage

Cartilage cord beneath the mucosa

Surgical Boundaries of the Maxillary Sinus

Caudal Limit Rostral border of orbit Rostral limit Line from rostral end of facial crest to infraorbital foramen Ventral boundary Facial crest Dorsal boundary Line from infraorbital foramen parallel to facial crest

Infundibulum

Centrally placed depression in the occlusal surface of an incisor

CLINICAL: Differences in Equine Lips

Commissures are rostral, not allowing the the oral cleft to be able to open widely --Clinical exam and intubation are difficult

When the dorsal conchal sinus and frontal sinus combine what do they form?

Conchofrontal sinus

Which type of teeth have cups vs. no cups?

Cups Incisors No Cups --Cheek teeth, molars and premolars --Infundibula are filled with cementum

Nasomaxillary opening

Curved slit b/w the dorsolateral wall of the skull and curved dorsolateral edge of ventral turbinate

What meatuses does the horse have?

Dorsal Middle Ventral Common

Apex: Equine

Dorsal cartilage does not project far laterally and ventrally (may be absent) No lateral support for apex

What supports the dorsal aspect of other species nose?

Dorsal lateral cartilages

Nuchal Crest

Dorsal projection of occipital bone

Location of Guttural Pouch

Dorsally B/w base of skull and atlas Ventrally B/w pharynx and start of esophagus Laterally Covered by pterygoid mm, parotid and mandibular glands

Which method of aging is more accurate?

Eruption dates

UNIQUE: Soft Palate

Exceptionally LONG --Except during deglutition its free border is wedged against the base of epiglottis --Causes rostral surface to lie against dorsal surface of soft palate Horse is unable to raise the soft palate

Landmarks of Skull

External sagittal crest Supraorbital foramen Nuchal crest Facial crest Nasoincisive notch

Eruption of Permanent Incisors

First Incisor 2.5 years Second Incisor 3.5 years Third Incisor 4.5 years

Nasal Septum

Forms a partition b/w nostrils, divides nasal cavity into right and left halves Caudal Portion Formed by perpendicular plate of ethmoid (osseous) Rostral Portion Cartilaginous and becomes more flexible towards the apex

What are the bones of the roof of the cranium in the ox?

Frontal bone only, it displaces the parietal bones laterally and caudally

Incisors

Func: To crop and cut grass --Table is flat, changes shape with age from oval to round, then back to oval

CLINICAL: Trephination Frontal Sinus

Halfway b/w medial angle of the eye and midline --Can also examine caudal maxillary sinus via frontomaxillary aperture

Cheek teeth and Incisors

High crowns, hypsodont Clinical Crown Part above the gum line Reserve Crown Proximal part in socket

How is the conchofrontal sinus drained?

Indirect drainage via the nasomaxillary opening to caudal maxillary sinus, into the nasal cavity

CLINICAL: What else does the longitudinal plate support?

Infraorbital canal, important if performing trephination of maxillary sinus to drain, DO NOT injure the nerve contained.

Frontomaxillary Opening

Large, oval, opening located on floor of sinus b/w median place and orbit Links frontal sinus directly w/ caudal maxillary sinus

CLINICAL: What teeth roots are in the maxillary sinus?

Last three cheek teeth, sockets occupy a greater proportion in younger animal

What supports the ventral and lateral aspect of other species nose?

Lateral accessory cartilage

Facial Crest

Laterally prominent ridge, most important landmark of the skull as it forms the boundaries of various sinuses

Nasoincisive Notch

Lies between the nasal and incisive bones

Supraorbital Foramen

Located in zygomatic process of frontal bone

How are the rostral and caudal sinuses further divided?

Longitudinal plate divides the ventral half of each sinus into a medial and lateral chamber

Equine Lips

Main prehensile organ of horse, mobile and sensitive

Premolars and Molars

Masticatory area is increased, w/ enlargement of premolar and assimilation with molars to create a continuous grinding surface

Compartments of the Guttural Pouch

Medial Walls Separated dorsally by the rectus capitis mm. and longus capitis mm. Caudal Part Folds over stylohyoid bone creating a small lateral compartment, and a large medial compartment

How does the maxillary sinus communicate with the nasal cavity?

Middle nasal meatus via the nasomaxillary opening

CLINICAL: Trephination Maxillary Sinus

Most often done to reach 3 molars for repulsion Dorsal Limit --To avoid nasolacrimal duct --Line b/w infraorbital foramen and medial palpebral commissure of eye Ventral Limit --Stay above root of teeth --Facial Crest

Auditive Tube

Narrow slit-like tube connecting tympanic cavity w/ nasopharynx --Osseous close to tympanic cavity --Cartilagenous towards the pharynx --Ends at nasopharynx w/ pharyngeal opening

What supports the medial aspect of other species nose?

Nasal septum (and rostral bone in pigs)

UNIQUE: Does the incisive duct open into the oral cavity in the horse?

No

Roof of the cranium

Occipital bone Parietal bone Interparietal bone Frontal bone rostrally

UNIQUE: What muscle of mastication is unique to the horse?

Occipitomandibularis, extends b/w paracondylar process of occipital bone to caudal border of mandible (#4') --Is an extra portion of the digastricus Innvervated: By facial nerve

When does the Seven-Year Hook appear?

Occurs as a result of uneven heat on upper corner incisor, and projects from distal aspect of occlusal surface --Appears at 7yrs --Disappears at 9 yrs --Reappears at 11 yrs

Drainage of Sinuses

Only rostral and caudal maxillary communicate directly w/ nasal cavity Ventral Conchal Sinus Drains into rostral maxillary Dorsal Conchal Sinus Drains into frontal sinus, to caudal maxillary sinus Sphenopalatine, and Middle Conchal Sinuses Drains into caudal Maxillary Sinus

What is the purpose of the occipitomandibularis muscle?

Opening the jaw

What is the function of the incisive duct?

Organ that controls sexual reproductive behavior by means of pheromones

Medial accessory cartilage

Other Species Small Horse Large and S-shaped Gives cartilagenous support to alar fold

Apex

Point of nose, supported by various cartilaginous structures, some species bony structures as well

EQUINE TONGUE

Poorly defined and short median sulcus/groove, thick --If pigmentation appears abnormal, indicative of malignant tumor

Apex: Carnivores and Porcine

Protrudes to some extent from face, and nostrils of apex lead into nasal cavity

What makes up the clinical root?

Reserve crown and true root

CLINICAL: Trephination of Rostral Maxillary Sinus and Caudal Maxillary Sinus

Rostral 25 mm dorsal to rostral end of facial crest, can also inspect ventral conchal sinus Caudal Same level, but towards caudal end of facial crest

Boundaries of Frontal Sinus

Rostral Mid-way between medial angle of the eye and rostral end of facial crest Medially Line 2 cm parallel to medial plane Laterally Ling passing through supraorbital foramen and parallel to medial limit Caudally Vertical line through middle of zygomatic arch

What does the ventral conchal sinus communicate with?

Rostral maxillary sinus

Nasal Septum: Carnivores, Procine, and Ruminants

Rostral part widest along dorsal and ventral margins So the dorsal and ventral lateral nasal cartilage will support lateral wall of apex

External Sagittal Crest

Runs cranially along the midline, and forms temoporal line on either side, before joining the zygomatic process of frontal bone

Nasolacrimal Duct

Runs on dorsolateral aspect of maxillary sinus, be careful to not injure it when performing surgical interventions in maxillary sinus

When does the dental star appear?

Starts as oval, moves more centered as cup disappears First Incisor 8 years (as a transverse line on vestibular surface All incisors 13 years it is centered 15 years, all stars are round

What supports the apex of the equine nose?

Support given dorsally, medially and ventrally by means of the alar cartilages, wing-like structure attached to rostral border of nasal septum (#9)

T/F there is NO communication b/w the two parts of the maxillary sinus?

True, they are completely separate

CLINICAL: Nasal diverticulum

Unique to horse --Blind dorsal cutaneous pouch extending rostrocaudally, created from the dorsal part of the alar fold --When passing a tube, can get caught

CLINICAL: Which meatus is used for stomach intubation?

Ventral meatus

CLINICAL: How can you tell the gutteral pouch is infected?

Viborg's triangle is swollen

CLINICAL: Nasomaxillary opening blockage

When inflamed, mucosa will block the slit and prevent drainage